This disclosure relates to a disposable thin wall core die, methods of manufacture thereof and articles manufactured therefrom.
Components having complex geometry, such as components having internal passages and voids therein, are difficult to cast using current commercial methods; tooling for such parts is both expensive and time consuming, for example, requiring a large lead-time. This situation is exacerbated by the nature of conventional molds comprising a shell and one or more separately formed cores, wherein the core(s) are prone to shift during casting, leading to low casting tolerances and low casting efficiency (yield). Examples of components having complex geometries that are difficult to cast using conventional methods include hollow airfoils for gas turbine engines, and in particular relatively small, double-walled airfoils. Examples of such airfoils for gas turbine engines include rotor blades and stator vanes of both turbine and compressor sections, or any parts that need internal cooling.
In current methods for casting hollow parts, a ceramic core and shell are produced separately. The ceramic core (for providing the hollow portions of the hollow part) is first manufactured by pouring a slurry that comprises a ceramic into a metal core die. After curing and firing, the slurry is solidified to form the ceramic core. The ceramic core is then encased in wax and a ceramic shell is formed around the wax pattern. The wax that encases the ceramic core is then removed to form a ceramic mold. The ceramic mold is then used for casting metal parts.
The slurry used to manufacture the ceramic core generally has a relatively high viscosity of about 105 to about 108 Pascal-seconds (Pa-s) when measured at room temperature. In order to ensure that the high viscosity slurry fills up all of the channels and interstices present in the metal core die, pressures greater than or equal to about 35 kilogram-force per square centimeter are used to inject the slurry into the core die. The use of such large pressures promotes the use of metal core dies having wall thickness of greater than or equal to about 15 millimeters. Such metal core dies are heavy, expensive to produce and the method of production is generally time-consuming. It is therefore desirable to improve the core die design so that core dies that are lighter in weight than the metal core dies can be produced. It is also desirable for these core dies to have thin walls that take advantage of low viscosity slurries (and hence lower operating pressures) for producing structures that have complex internal shapes.